The goal of the research program is to define the molecular mechanisms involved in the replication of enveloped RNA viruses. In particular, the specificity requirements governing the interaction of RNA and protein molecules during viral assembly will be studied in a system which is known to produce defective murine leukemia virus particles containing low molecular weight RNA, but not the high molecular weight 70S RNA genome. Experiments will be carried out to further characterize virion RNA and to determine whether this RNA is derived from the host or whether a portion is virus-specific. In addition, the properties of the reverse transcriptase enzyme contained in the defective particles will be examined.